env do |env|
  env["CPPPATH"] << "src/two"
  env.Object("one.o", "src/one/one.c")
  env.add_post_build_hook do |builder|
    if builder.target == "one.o"
      env["MODULE"] = "two"
      env.Object("${MODULE}.o", "src/${MODULE}/${MODULE}.c")
    end
  end
end